The Old Guard is the nickname for the 3rd U.S. Infantry Regiment, the oldest active-duty infantry unit in the Army, with its beginnings dating to 1784. It duties include standing sentinel at the Tomb of the Unknown Soldier, which Cotton said he did as well.

"One common phrase I hear is that the unknowns didn't just give up their life, they gave up their identities," he said. "We'll never know who they are – and when you think about that kind of sacrifice in the service of our nation, what is it to sacrifice a night's worth of sleep?"

"I think is a lesson that all readers will be able to take away from 'Sacred Duty' . . . [is that] in every walk of life, in every job we have, we can all strive for that kind of standard of excellence and always strive to be our very best self."

Cotton told the story of one soldier, Staff Sgt. Adam Dickmyer, 26, whose service with the Old Guard preceded Cotton's — and who went back to combat and was killed Oct. 28, 2010, in Kandahar, Afghanistan, by a roadside bomb.

"To this day, the Tomb of the Unknown Soldier platoon honors him in ways large and small," Cotton said. "They have a headstone rubbing of his headstone inside their quarters. Every year on the anniversary of his death . . . they put out two dimes and a penny as a symbol of 21 (gun salute), one the highest tribute our nation can pay to its fallen."

There is even a replica of his uniform on a mannequin inside the Tomb of the Unknown Soldier, he said.

"And I think that silent tribute to Staff Sgt. Dickmeyer . . . Is a perfect encapsulation of the kind of honor that the Tomb guards and all Old Guard soldiers pay our nation's fallen — that we will never forget their sacrifice," he said.

There were "few more honorable" missions on which Sen. Tom Cotton, R-Ark., served than his time in the Army's "Old Guard" at Arlington National Cemetery, the war veteran told Newsmax TV's "Newsmax Now."

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